JOSEPHINE YAGA of NARI
Soil fertility in the Highlands of PNG has been declining for sometime primarily due to potassium deficiency, resulting in impaired sweet potato production with old gardens abandoned in most communities.
Sulphur and phosphorus deficiencies are also important for sweet potato production in both old and new gardens.
This is according to a technical bulletin published by the National Agricultural Research Institute (NARI) last December .
Factors contributing to nutrient depletions from the garden systems were removal of phosphorus and sulphur-rich vines from cultivation area, shortening of fallow periods, and burning of weed and crop residues.
A scoping study on soil fertility in 2005 by NARI confirmed that low yields in the Highlands were associated with suboptimal nutrient uptake by the crop, despite high apparent nutrient stock.
The publication, titled “An evaluation of soil fertility constraints in the Highlands of Papua New Guinea”, further states that action is urgently needed to reverse the trend if basic food and income requirements of the Highland’s population are to be met.
In order to address the problem, the book recommends that nutrients most limiting to crop production in different situations and regions must first be identified.
It points out that the indigenous practice of heaping compost materials in the centre of soil mounds on which sweet potato is cultivated is a good strategy.
This is a common practice on sweet potato production in Enga and parts of the Western Highlands province.
The mounds effectively hold compost-derived nutrient cations and the practice has merit to be promoted throughout Western Highlands, Enga and Simbu.
NARI is currently undertaking a project on soil fertility management in the PNG Highlands for sweet potato-based cropping systems.
The objective is to conduct process studies to fill critical knowledge gaps in soil water and nutrient dynamics in relation to the growth cycle of sweet potato.
It is a collaborative project between the Lutheran Development Services with funding support from the Australian Centre for International Agricultural Research.
The studies are undertaken at Aiyura in Eastern Highlands, Kondiu in Simbu and Tambul in the Western Highlands.